(a) Technical Field
The present invention relates to a display device including a touch sensor and a manufacturing method thereof, and particularly, to a display device including a touch sensor using a piezoelectric material and a manufacturing method thereof.
(b) Description of the Related Art
A display device (such as liquid crystal display (LCD), organic light emitting diode display (OLED display), or electrophoretic display) includes an electric field generating electrode and an electro-optical active layer. An LCD may include a liquid crystal layer as the electro-optical active layer; an OLED display may include an organic light emitting layer as the electro-optical active layer, and an electrophoretic display may include a layer having charge-carrying particles as the electro-optical active layer. The electric field generating electrode may be connected to a switching element (e.g. a thin film transistor). When a data signal is applied to the switching element, the electro-optical active layer displays an image by converting the data signal to an optical signal.
In addition to the image display function, a display device may include a touch sensing function. The touch sensing function allows a user to interact with the display device when contact information is received (or sensed) from the user. For example, a display device having a touch sensing function can detect whether an object has approached or made physical contact with the screen of the display device, as well as the actual contact position on the screen (if contact has been made). The touch sensing function may be accomplished using, for example, a touch sensor to sense the change in pressure, charge, or reflected light in the display device when a user touches the screen with a finger or touch pen. The sensed information is then converted into an image signal for displaying an image on the display device.
The touch sensor may include resistive sensors, capacitive sensors, electro-magnetic (EM) sensors, optical sensors, or other types of sensors.
A capacitive touch sensor may include a sensing capacitor having a sensing electrode capable of transferring a sensing signal. Specifically, the capacitive touch sensor can detect whether contact has been made and the actual contact position, by sensing the change in capacitance of the sensing capacitor when a conductive element (such as the user's finger) approaches the sensor.
In a resistive touch sensor, a pair of electrodes spaced apart may come into contact due to external pressure from an object. When the two electrodes make contact at a particular position, the resistance of the electrodes changes. The contact position is then determined by measuring the corresponding change in voltage.
The resistive touch sensor typically works well for a single point of contact. However, if a user simultaneously touches a plurality of points on the screen of the display device, the resistive touch sensor may not be able to obtain touch information pertaining to the plurality of points since the voltages registered across the points are the same. A capacitive type touch sensor may be capable of obtaining information pertaining to a plurality of points. However, the capacitive type touch sensor may not be able to obtain contact information if an insulator makes contact with the screen (e.g. when a user is wearing hand-gloves).
In some cases, it may be useful if the display devices can sense contact strength in addition to contact position. Contact strength refers to the amount of pressure that a user applies on a particular spot on the screen of the display device. However, conventional display devices including the above touch sensors may lack the capability of sensing both contact position and contact strength.